Messier 54

Messier 54
Messier 54
Messier 54 Hubble WikiSky.jpg
M54 by Hubble Space Telescope; 3.5′ view
Credit: NASA/STScI/WikiSky
Observation data (J2000 epoch)
Class III
Constellation Sagittarius
Right ascension 18h 55m 03.28s[1]
Declination -30° 28′ 42.6″[1]
Distance 87.4 kly[2] (26.8 kpc)
Apparent magnitude (V) 8.37[1]
Apparent dimensions (V) 12′.0
Physical characteristics
Radius 153 ly[3]
Estimated age 13 Gyr[4]
Notable features Probably extragalactic
Other designations M54,[1] NGC 6715,[1] GCl 104[1]
See also: Globular cluster, List of globular clusters

Messier 54 (also known as M54 or NGC 6715) is a globular cluster in the constellation Sagittarius. It was discovered by Charles Messier in 1778 and subsequently included in his catalog of comet-like objects.

Previously thought to belong to our Galaxy at a distance from Earth of about 50,000 light-years, it was discovered in 1994 that M54 most likely belongs to the Sagittarius Dwarf Elliptical Galaxy, (SagDEG),[5] making it the first globular cluster formally thought to be part of our galaxy reassigned to extragalactic status, even if not recognized as such for nearly two and a quarter centuries.

Modern estimates now place M54 at a distance of some 87,000 light-years, translating into a true radius of 150 light-years across. It is one of the denser of the globulars, being of class III (I being densest and XII being the least dense). It shines with the luminosity of roughly 850,000 times that of the Sun and has an absolute magnitude of -10.0.

M54 is easily found on the sky, being close to the star ζ Sagittarii. It is however, not resolvable into individual stars even with larger amateur telescopes.

In July 2009, a team of astronomers reported that they had found evidence of an intermediate-mass black hole in the core of M54.[6]

See also

References

  1. ^ a b c d e f "SIMBAD Astronomical Database". Results for NGC 6715. http://simbad.u-strasbg.fr/Simbad. Retrieved 2006-11-16. 
  2. ^ Gavin Ramsay; Kinwah Wu (2005). "Chandra observations of the globular cluster M54". arXiv:astro-ph/0510217 [astro-ph]. doi:10.1051/0004-6361:20053855. 
  3. ^ distance × sin( diameter_angle / 2 ) = 153 ly. radius
  4. ^ Geisler, Doug; Wallerstein, George; Smith, Verne V.; Casetti-Dinescu, Dana I. (2007). "Chemical Abundances and Kinematics in Globular Clusters and Local Group Dwarf Galaxies and Their Implications for Formation Theories of the Galactic Halo". Publications of the Astronomical Society of the Pacific 119 (859): 939–961. Bibcode 2007PASP..119..939G. doi:10.1086/521990. 
  5. ^ Siegel, Michael H.; Dotter, Aaron; Majewski, Steven R.; Sarajedini, Ata; Chaboyer, Brian; Nidever, David L.; Anderson, Jay; Marín-Franch, Antonio et al. (2007). "The ACS Survey of Galactic Globular Clusters: M54 and Young Populations in the Sagittarius Dwarf Spheroidal Galaxy". Astrophysical Journal Letters 667 (1): L57-L60. Bibcode 2007ApJ...667L..57S. doi:10.1086/522003. 
  6. ^ Ibata, R.; Bellazzini, M.; Chapman, S. C.; Dalessandro, E.; Ferraro, F.; Irwin, M.; Lanzoni, B.; Lewis, G. F. et al. (2009). "Density and Kinematic Cusps in M54 at the Heart of the Sagittarius Dwarf Galaxy: Evidence for a 104 M Black Hole?". Astrophysical Journal Letters 699 (2): L169-L173. arXiv:0906.4894. Bibcode 2009ApJ...699L.169I. doi:10.1088/0004-637X/699/2/L169. 

External links

Coordinates: Sky map 18h 55m 03.28s, −30° 28′ 42.6″


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